The present invention related to a pneumatic laminar motor, for dental purposes, consisting of a sleeve-like housing forming the stator, with circular cylindrical inside wall and a rotor arranged within and contacting this inside wall. This rotor has a diameter smaller than the inside wall of the circular cylinder and its axis of rotation runs parallel to the axis of the inside wall of the circular cylinder and is displaced from it. The lengthwise slots of the rotor has radially movable lamellas with their outer ends pointing to the circular cylindrical inside wall. An air inlet opening for the compressed air, coming from a compressed air supply conduit, and an air outlet opening discharge into the space between rotor and circular cylindrical inside wall. Between the circular cylindrical inside wall and the outer ends of the lamellas there is located a bearing ring which is freely rotatable relative to the inside wall and which is coaxial with the inside wall. The outer ends of the lamellas contact the bearing ring. When compressed air is applied to the motor, it enters through the air inlet openings(s) into the space between rotor and circular cylindrical inside wall and pushes the nearest lamella protruding furtherest from the rotor ahead of it so that the rotor starts to turn and the next lamella is charged by the compressed air. The speed of the laminar motor may run between 20,000 and 100,000 rpm. The outer lamella ends contact the freely rotatable bearing ring and are to be protected in this manner against any sliding friction the bearing ring participates in the rotation of the rotor due to static friction of the outer lamella ends at the inside of the bearing ring.
Such a laminar (or lamellar) motor is known from the German Laid-Open Document No. 26 21 486. The air inlet opening(s) in this known laminar motor discharge axially, i.e., from one motor face side into the space between rotor and circular cylindrical inside wall. Therefore, the location of the compressed air inlet conduit up to this radial entry is relatively complicated. Not only because of this axial discharge by itself, but also because of the small dimensions of the laminar motor required for dental handpieses, the throughflow of air per unit of time is relatively low so that difficulties arise when starting the motor. On the other hand it has been found that the desired rotation participation of the bearing ring caused by the outer lamella ends does not always take place, even though the inside wall of the bearing ring of this known laminar motor has axial grooves of a flat curved cross section to receive the outer ends of the lamellas. Because of the flatness of the grooves and the troubles and impediments caused by the aforementioned difficulties during the buildup of an air cushion between bearing and circular cylindrical housing inside wall and because of a restriction of the free rotation of the bearing ring, the lamella ends slide out of the grooves during certain operation modes and/or shift or bend such that the performance of the motor deteriorates appreciably.